These can be used to give an unswitched lampholder a little extra height on the top of a Standard lamp.  For example, for repairing a wooden standard lamp, fix a 1/2 flange plate to the top of the lamp. Use a 1/2 locknut cover to give neat finish, then screw this 1/2 coupler to the flange plate.  Then thread a 1/2" brass all thread 3/4" length into coupler. This leaves the correct amount of thread protruding to fix a half inch lampholder to.  The result is stunning.